Permeable Pavement

[MiguelPenaWSE]

Good afternoon Engineers!

I am currently working on the design of a flexible permeable pavement, (first time doing so). The reason to implement this material is to minimize, even eliminate, stormwater runoff.

According to TxDOT, I was able to come up with most variables except the Mr (Resilient Modulus) for the two-layer system.

The in-situ soil is a Sandy Soil (USC Soil Type SM).
I can easily come up with Mr if I were to follow the following equations;
1) Mr = 2555 x (CBR)^0.64
2) Mr = 1500 x (CBR)

The problem I am running into is that I can not get accurate and/or reliable CBR values for (1) No.57 aggregate with 40% void ratio for the reservoir layer and (2) the flexible permeable top layer.
Also, the Mr values do change depending on the Wet and Dry season.
Any guidance related to the change due to wet/dry season would be appreciated.

Thank you so much!

 

[Ron]

You will have to get the reservoir layer tested for CBR. For the asphalt layer, find a Mr for an open graded friction course...will likely be close. Since your permeable layer also serves as a structural layer, you might have a need for more thickness than you might think, depending on traffic.

Also, I would caution against thinking you will have no runoff. Pervious pavements get overwhelmed quickly in short duration, high intensity rainfall so runoff is inevitable. Further, debris infiltation will clog the pervious pavement with time and you will have even more runoff.

Great to get you through an approval process.....not so much for long term performance.